Protector for electric circuits

ABSTRACT

An electric fuse, which can carry current continuously in a location where the temperature is quite high, has a fusible element that is enclosed by, but that can freely expand and contract relative to, a tubular casing. That fusible element is a metal stamping of rectangular cross section; and hence it will respond to temperature-induced elongation thereof to deflect in a plane which is disposed at right angles to the wide surface thereof. The fusible element is relieved of potentially hurtful stresses by making the inner radius of the tubular casing at least as great as the square root of the sum of (W/2)2 and ((D/2+T/2))2, where T is the thickness of the fusible element, where W is the width of that part of the fusible element which is enclosed by the tubular casing and which would be the first part of the fusible element that could respond to deflection of the fusible element, toward the inner surface of the tubular casing, to engage that inner surface, and where D is the maximum deflection which that part of the fusible element could experience if the edges of the uppermost surface of that part were in engagement with one side of the inner surface of the tubular casing prior to the start of the deflection and if the edges of the lowermost surface of that part were in engagement with the opposite side of the inner surface of the tubular casing at the conclusion of that deflection. The ends of the fusible element have configurations which limit axial movement of adjacent portions of the fusible element inwardly of the tubular casing.

United States Patent [191 McAlister PROTECTOR FOR ELECTRIC CIRCUITS [76] Inventor: Craig L. McAlister, 8951 Midland,

St. Louis, Mo. 63114 22 Filed: June 14, 1973 21 Appl. No.: 369,869

Primary Examiner-Roy N. Envall, Jr. Attorney, Agent, or FirmRogers, Ezell & Eilers [57] ABSTRACT An electric fuse, which can carry current continuously in a location where the temperature is quite high, has a fusible element that is enclosed by, but that can freely expand and contract relative to, a tubular cas- [451 Apr. 16, 1974 ing. That fusible element is a metal stamping of rectangular cross section; and hence it will respond to temperature-induced elongation thereof to deflect in a plane which is disposed at right angles to the wide surface thereof. The fusible element is relieved of potentially hurtful stresses by making the inner radius of the tubular casing at least as great as the square root of the sum of (W/2) and [(D/2+T/2)] where T is the thickness of the fusible element, where W is the width of that part of the fusible element which is enclosed by the tubular casing and which would be the first part of the fusible element that could respond to deflection of the fusible element, toward the inner surface of the tubular casing, to engage that inner surface, and where D is the maximum deflection which that part of the fusible element could experience if the edges of the uppermost surface of that part were in engage-- ment with one side of the inner surface of the tubular casing priorto the start of the deflection and if the edges of the lowermost surface of that part were in engagement with the opposite side of the inner surface of the tubular casing at the conclusion of that deflection. The ends of the fusible element have configurations which limit axial movement of adjacent portions of the fusible element inwardly of the tubular casing.

15 Claims, 16 DrawingFigures 'PATENTEDAPR 16 m4 SHEET 1 OF 2 FIG. 2.

FIG.

'lI/UAII .1111! IIIIIA PROTECTOR FOR ELECTRIC CIRCUITS This invention relates to improvements in Protectors For Electric Circuits. More particularly, this invention relates to improvements in electric fuses which can carry their rated currents continuously in locations where the temperatures are quite high.

It is, therefore, an object of the present invention to provide an electric fuse which can carry its rated current continuously in a location where the temperature is quite high.

When an electric fuse is used in a location where the temperature is quite high, all portions of the fusible element of .that electric fuse will experience appreciable expansion; and that expansion will be distinctly greater than the expansion of the tubular casing for that fusible element. If the fusible element of such an electric fuse were to be positively and fixedly secured to the tubular casing for the fusible element as is usually done with electric fuses that are to be used in relatively cool locations, the relatively greater expansion of that fusible element could cause undesirable stresses to develop within that fusible element. The present invention makes it possible to use an electric fuse in a location where the temperature is quite high by mounting the tubular casing for the fusible element of that electric fuse so relative movement can freely occur between that fusible element and that tubular casing. Further, the present invention makes the inner diameter of the tubular casing large enough to permit portions of the fusible element to freely deflect toward the inner surface of that tubular casing and thereby compensate, at least in part, for the temperature-induced elongation of that fusible element. Moreover, the present invention makes the fusible element rectangular in cross section so the deflection of that fusible element toward the inner surface of the tubular casing is limited to a plane that is disposed at right angles to the wide surface of that fusible element. It is, therefore, an object of the present invention to provide an electric fuse wherein the tubular casing for the fusible element of that electric fuse is mounted to permit free relative movement between that fusible element and that tubular casing, to make the inner diameter of that tubular casing large enough to permit portions of that fusible element to freely deflect toward that inner surface of that tubular casing and thereby compensate, at least in part, for the temperature-induced elongation of that fusible element, and to make that fusible element rectangular in cross section.

The inner radius of the tubular casing of the electric fuse provided by the present invention is at least asgreat as the square root of the sum of (W/2) and [(D/2)+(T/2)]hu 2. where T is the thicknessof the fusible element, where W IS the width of that part of the fusible element which is enclosed by the tubular casing and which would be the first part of the fusible element that could respond to deflection of the fusible element, toward the inner surface of the tubular casing, to engage that inner surface, and where D is the maximum deflection which that part of the fusible element could experience if the edges of the uppermost surface of that part were in engagement with one side of the inner surface of the tubular casing prior to the start of the deflection and if the edges of the lowermost surface of that part were in engagement with the opposite side of the inner surface of the tubular casing at the conclusion of that deflection As a result, temperature-induced elongation of that fusible element cannot develop hurtful stresses within that fusible element. It is, therefore, an object of the present invention to provide an electric fuse wherein the inner radius of the tubular casing is at least as great as the square root of the sum of (W/2) and [(D/2) +(T/2)] where T is the thickness of the fusible element, where W is the width of that part of the fusible element which is enclosed by the tubular casing and which would be the first part of the fusible element that could respond to deflection of the fusible element, toward the inner surface of the tubular casing, to engage that inner surface, and where D is the maximum deflection which that part of the fusible element could experience if the edges of the uppermost surface of that part were in engagement with one side of the inner surface of the tubular casing prior to the start of the deflection and if the edges of the lowermost surface of that part were in engagement with the opposite side of the inner surface of the tubular casing at the conclusion of that deflection.

THe fusible element of the electric fuse provided by the present invention has end portions which are disposed outwardly of the ends of the tubular casing for that fusible element; and those end portions have configurations which enable those end portions to coact with the ends of the tubular casing to limit axial movement of adjacent portions of that fusible element inwardly of that tubular casing. As a result, the end portions of the fusible element prevent accidental separation of that fusible element from the tubular casing for that fusible element even though that fusible element is able to move axially relative to that tubular casing. It is, therefore an object of the present invention to provide an electric fuse with a fusible element that has end portions which are disposed outwardly of the ends of the tubular casing for that fusible element and which have configurations that enable those end portions to coact with the ends of that tubular casing to limit axial movement of adjacent portions of that fusible element inwardly of that tubular casing.

The fusible element of one electric fuse provided by the present invention has a portion of reduced cross section which serves as a weak spot, and it has intermediate portions which extend axially outwardly from that portion of reduced cross section to merge into the end portions of that fusible element. Those intermediate portions subdivide the ends of the tubular casing for that fusible element into narrow passages which have the opposite faces of those intermediate portions defining the inner walls thereof and which have the inner surface of that tubular casing defining the outer walls thereof. When any gases or vapors pass outwardly of the tubular casing as the weak spot blows, those gases and vapors will be cooled by being forced to engage the opposite faces of the intermediate portions and also by being forced into engagement with the inner surfaces of the ends of the tubular casing. The intermediate portions of the fusible element of the present invention are relatively long; and the consequent relative lengths of the narrow passages defined by those intermediate portions assure desirable cooling of any gases or vapors which pass outwardly of the tubular casing as the weak spot blows. It is, therefore, an object of the present invention to provide an electric fuse with a fusible element which has intermediate portions that are disposed outwardly of the weak spot of that electric fuse and which subdivides the ends of the tubular casing for that fusible element into relatively long passages of narrow cross section.-

Other and further objects and advantages of the present invention should become apparent from an exami nation of the drawing and accompanying description.

In the drawing and accompanying description, several preferred embodiments of the present invention are shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, FIG. 1 is a plan view, on a large scale, of one form of fusible element, for an electric fuse, that is made in accordance with the principles and teaching of the present invention, and it shows the right-hand end of that fusible element bent to have a U-shaped cross section;

FIG. 2 is an elevational view, on the scale of FIG. 1, of the right-hand end of the fusible element of FIG. 1;

FIG. 3 is a sectional view, on the scale of FIG. 1, through a tubular casing which encloses the fusible element of FIG. 1 after the right-hand end of the fusible element has been planished;

FIG. 4 is a sectional view, on a still larger scale, through the fusible element and tubular casing of FIG. 3, and it is taken along the plane indicated by the line 4-4 in FIG. 3;

FIG. 5 is a longitudinal section, on the scale of FIG. 3 but at ninety degrees from the longitudinal section of FIG. 3, of the fusible element and tubular casing of FIG. 3, and it shows that fusible element in an elongated state;

FIG. 6 is a sectional view, on the scale of FIG. 4, through the fusible element and tubular casing of FIG. 3, and it is taken along the plane indicated by the line 66 in FIG. 5;

FIG. '7 is a partially broken-away bottom view of a frying pan in which the fusible element and tubular casing of FIG. 3 are incorporated, and that tubular casing is shown approximately to scale;

FIG. 8 is a partially broken-away view of a winding which is mounted on an iron core and which has the tubular casing and fusible element of FIG. 3 incorporated within it;

FIG. 9 is a partially broken-away view of a container in which a capacitor and the tubular casing and fusible element fuse of FIG. 3 are mounted;

FIG. 10 is an elevational view of the fusible element and tubular casing of FIG. 3 as they are supportd by conductors within the envelope of an electric lamp;

FIG. 11 is a longitudinal section through another tubular casing and fusible element for an electric fuse;

FIG. 12 is a longitudinal section through still another tubular casing and fusible element for an electric fuse;

FIG. 13 is a longitudinal section through a further tubular casing and fusible element for an electric fuse;

FIG. 14 is a longitudinal section through a still further tubular casing and fusible element for an electric fuse;

and

FIG. 16 is a section through the tubular casing and fusible element of FIG. 14, and it is taken along theplane indicated by the line 1616 in FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1-6 and 10, the numeral 11 generally denotes a fusible element, for an electric fuse, which has a terminal-like end portion 12, an intermediate portion 14, a portion 16 of reduced cross section that serves as a weak spot, a second intermediate portion 18, and a second terminal-like end portion 20. As shown particularly by FIGS. 1 and 2, the edges 22 of the terminal-like end portion 20 are initially bent upwardly to give that terminal-like end portion a U- shaped configuration. In one embodiment of the present invention, the fusible element 11 is a stamping which is made from nickel, which is rectangular in cross section, which has an overall length of between seven hundred and fourteen thousandths and seven hundred and twenty-four thousandths of an inch, and which has a constant thickness between forty-eight tenthousandths and fifty-two ten-thousandths of an inch. Each of the terminal-like end portions 12 and 20 is between ninety-eight thousandths and one hundred and two thousandths of an inch wide and between one hundred and twenty thousandths and one hundred and thirty thousandths of an inch long. The portion 16 of reduced cross section is between fifteen thousandths and seventeen thousandths of an inch wide, and it is approximately one-half of the length of either of the terminal-like end portions 12 and 20. Each of the interme diate portions 14 and 18 is between fifty-eight thousandths and sixty-two thousandths of an inch wide and it is approximately twice as long as either of the terminal-like end portions 12 and 20. The exact length of the portion 16 of reduced cross section will be a function of the electrical characteristics desired for the fusible element; and that portion can be lengthened by shortening the lengths of the intermediate portions 14 and The numeral 24 denotes a tubular casing of insulating material; and a ceramic material or glass is useful in making that tubular casing. In the said embodiment of the present invention, the tubular casing 24 is between four hundred and twenty-three thousandths and four hundred and fifty-three thousandths of an inch long, has an outer diameter between ninety-seven thousandths and one hundred and two thousandths of an inch, and has an inner diameter of between sixty-three thousandths and sixty-seven thousandths of an inch.

The inner diameter of the tubular casing 24 thus averages only about five thousandths of an inch greater than the width-of either of the intermediate portions 14 and 18 of the fusible element 11. Consequently, when the tubular casing 24 is telescoped over the bent terminal-like end portion 20 of the fusible element 11, the inner surface of that tubular casing will be close to or will engage one edge of the intermediate portion 14 and one edge of the intermediate portion 18, as shown particularly by FIG. 3. The opposite side of that inner surface of that tubular casing will engage or be close to the opposite edge of the intermediate portion 14 and the opposite edge of the intermediate portion 18. Consequently, as shown particularly by FIG. 4, the intermediate portion 18 will subdivide the space within the right-hand end of the tubular casing 24 into two small, generally semi-cylindrical spaces which are only about sixty-five thousandths of an inch wide and less than thirty-two thousandths of an inch deep. The opposite faces of the intermediate portion 18 will define the inner walls of those two generally semi-cylindrical spaces, and the inner surface of the right-hand end of the tubular casing 24 will define the outer walls of those semi-cylindrical spaces. Similarly, the intermediate portion 14 will subdivide the left-hand end of the tubular casing 24 into two small, generally semi-cylindrical spaces which are only about sixty-five thousandths of an inch wide and less than thirty-two thousandths of an inch deep. The opposite faces of the intermediate portion 14 will define the inner walls of those two generally semi-cylindrical spaces, and te inner surface of the lefthand end of the tubular casing 24 will define the outer walls of those semi-cylindrical spaces.

The edges 22 of the right-hand terminal-like end portion of the fusible element 11 are initially bent to have convex outer faces so they can readily be telescoped through the tubular casing 24-. After the terminal-like end portion 20, the intermediate portion 18, the portion 16 of reduced cross section, and the intermediate portion 14 have been successively telescoped into the tubular casing 24, and'after the terminal-like end portion 20 has been extended beyond the opposite end of that tubular casing, that terminal-like end por tion will be planished to have the configuration shown by FIG. 3. At such a time, the fusible element 11 and the tubular casing 24 will coact to constitute a partiallyenclosed cartridge-type electric-fuse 26. Both ends of the tubular casing 24 will be open; andthat tubular casing will be able to respond to gravity to move relative to the fusible element 11. Also, the intermediate portions 14 and 18 will be able to move relative to the adjacent ends of the tubular casing 24 as the fusible element 1 l elongates and contracts relative to that tubular casing in proportion to the relative thermal coefficients of expansion of the materials of that fusible element and of that tubular casing. Because the end portions 12 and 20 are disposed outwardly of the ends of the tubular casing 24, and because each of those end portions is wider than the inner diameter of the adjacent end of the tubular casing 24, those end portions will coact with those ends to limit axial shifting of that tubular casing relative to that fusible element. Consequently, those end portions force the tubular casing 24 to overlie and protect the weak spot 16 even though those end portions permit limited axial shifting of that tubular casing relative to the intermediate portions 14 and 18.

Because the fusible element is made from nickel, the electric fuse 26 will be able to carry its rated current continuously, even when that electric fuse is operated in a excation where high temperature conditions exist. For example, that electric fuse will be able to carry its rated current continuously, even when it is incorporated into a device such as the frying pan 28 of FIG. 7. That frying pan has an electrical heating element 30 of standard and usual design; and one end of the resistance element 34 of that electrical heating element is connected to the end portion 12 of the fusible element 11 by a conductor 35. The other end of the resistance element 34 is connected to a stiff lead-in conductor 37 of the frying pan 28; and the end portion 20 is connected to a stiff lead-in conductor 32 of that frying pan. Although the end portions 12 and 20 of the electric fuse 26 could be secured, respectively, to the conductor 35 and to the lead-in conductor 32 in various ways, those end portions will preferably be secured to those conductors by welding.

As long as the current flowing through the electrical heating element 30 of the frying pan 28 does not substantially exceed the rated current of the electric fuse 26, the weak spot 16 will not fuse. However, that weak spot, the intermediate portions 14 and 18, the end portions 12 and 20, and the tubular casing 24 can respond to the heat generated by the electrical heating element 30 to become quite hot. Because the thermal coefficient of expansion of nickel is greater than the thermal coefficient of expansion of glass or of ceramic material, the fusible element 11 will elongate to a greater extent than will the tubular casing 24 the difference between the extents of elongation being proportional to the difference between those thermal coefficients of expansion. I

When the fusible element 11 and the tubular casing 24 are at room temperature, the ends of that tubular casing will be close to, although spaced axially outwardly of, the confronting edges of the terminal-like end portions 12 and 20. As the temperatures of that fusible element and of that tubular casing rise, that tubular casing will be able to elongate freely, but the connectors 32 and 35 will impede elongation of that fusible element. If the ocnductors 32 and 35 are sufficiently stiff to be essentially rigid and immovable, any elongation of the fusible element 11 will have to be compensated for by a bending or bowing of that fusible element. As indicated by FIG. 5, the end portions 12 and 20 will remain essentially coplanar in large part because they are directly secured to the conductors 32 and 35; and hence the bending will be effectively confined to the intermediate portions 14 and 18 and the portion 16 of reduced cross section. Because those intermediate portions are wider, and thus have larger cross sections, than the portion 16 of reduced cross section, those intermediate portions tend to be more resistant to bending than is the portion 16 of reduced cross section; but, as shown by FIG. 5, those intermediate portions start bending immediately adjacent the confronting edges of the end portions 12 and 20, and thus start bending adjacent the ends of the tubular casing 24.

If the frying pan 28 is disposed so the conductors 32 and 35 define a horizontally-directed plane, as indicated by FIG. 5, the fusible element 11 will be horizontally directed; and the tubular casing 24 will normally have the upper area of the inner surface thereof resting upon the side edges of the uppermost surfaces of the intermediate portions 14 and 18. If temperatureinduced elongation of the fusible element 1 1 causes the longitudinal center of the portion 16 of reduced cross section to deflect upwardly, as indicated by FIG. 5, the upwardly-deflecting confronting ends of the intermediate portions 14 and 18 will engage the upper area of the inner surface of the tubular casing 24 and raise that tubular casing upwardly. On the other hand, if temperature-induced elongation of that fusible element causes the longitudinal center of the portion 16 to deflect downwardly, the upper area of the inner surface of the tubular casing 24 will rest upon the outer ends of the intermediate portions 14 and 18; and hence that tubular casing will tend to remain close to its initial position. In either event, any and all temperature-induced relative movement between the outer ends of the intermediate portions 14 and 18 and the ends of the tubular casing 24 can occur relatively freely because that tubular casing has both ends thereof open.

Where the fusible element of an electric fuse is equipped with a weak spot, and where that fusible element is installed in a location wherein the temperature is close to or below the temperature of the air external of that location, most of the heat-induced expansion and contraction of that fusible element occurs in and adjacent to the weak spot of that fusible element. As a result, the temperature-induced elongation of fusible elements usually is quite limited, and does not usually enforce appreciable deflection of the longitudinal centers of those fusible elements. However, the fusible element 11 of FIGs. 1-6 is made so it can be used in a location where the temperature could reach a value of 500 centigrade; and, when that fusible element is used in such a location, essentially all portions of the length thereof will experience temperature-induced elongation. To keep any such temperature-induced elongation from creating hurtful stresses within that fusible element, the inner diameter of the tubular casing 24 of insulating material is made large enough to permit the longitudinal center of the portion 16 of that fusible element to deflect without jamming any portions of that fusible element solidly against the inner surface of that tubular casing. Specifically, the radius of the inner surface of the tubular casing 24 should equal or exceed the square root of the sum of (w/2 +[(D/2 +(T/2)] where T is the thickness of the fusible element 11, where W is the width of the intermediate portion 14, and where D is the maximum deflection which the Iongitudinal center of the portion 16 could experience if the edges of the uppermost surface of that portion were in engagement with one side of the inner surface of the tubular casing 24 prior to the start of the deflection and if the edges of the lowermost surface of that portion were in engagement with the opposite side of the inner surface of that tubular casing at the conclusion of that deflection. Because the fusible element 11 is rectangular in cross section, the deflection of the longitudinal center of the portion 16 thereof will be in a plane at right angles to the wide surfaces of that portion.

The terminal-like end portions 12 and will be held against tilting or shifting by the bonding thereof to the conductors and 32; and hence any deflection of the fusible element 11 will be limited to the intennediate portions 14 and 18 and to the portion 16 of reduced cross section, as shown by FIG. 5. That deflection will start adjacent the opposite ends of the tubular casing 24, and will cause the fusible element 11 to assume a generally smooth and generally continuous arcuate configuration even though each of the intermediate portions 14 and 18 is stiffer than the portion 16. Because each of the intermediate portions 14 and 18 is wider than the elongated portion 16, the side edges of those intermediate portions will tend to engage the inner surface of the tubular casing 24 before any of the side edges of that elongated portion can engage that inner surface as indicated by FIG. 6. This is desirable because it keeps that elongated portion from being jammed against that inner surface.

As long as the current flowing through the fusible element 11 does not materially exceed the rated current of the electric fuse 26, that fusible element will remain intact; and repeated elongations and contractions of that fusible element will not impair or adversely affect that fusible element. However, if a short circuit were to develop within the electrical heating element 30, or if a relatively low resistance ground were to develop between the conductor of that electrical heating element and the casing of that electrical heating element, the amount of current flowing through the fusible element 11 would increase sharply; and the amount of heat generated by the weak spot 16 would be greater than the amount of heat'which the intermediate portions 14 and 18, the end portions 12 and 20, and the tubular casing 24 could absorb. Thereupon, the weak spot 16 would fuse and open the circuit. As that weak spot fused, an arc would develop between the confronting faces of the intermediate portions 14 and 18; and any gases and metal vapors which were created by that are and which would tend to issue from the tubular casing 24 would have to pass through the small semi-cylindrical spaces which are defined by the opposite faces of the intermediate portions 14 and 18 and the confronting inner walls of the ends of the tubular casing 24. As those gases and metal vapors passed through those small semi-cylindrical spaces, they would be cooled by direct and immediate contact with those opposite faces of those intermediate portions, and also by direct and immediate contact with those inner walls of the ends of that tubular casing. The cooling of those gases and metal vapors would be desirable because it would tend to limit the pressures which could build up adjacent the electric fuse 26.

Referring to FIG. 8, the numeral 36 denotes an iron core which has a winding 38 of standard and usual form on one leg thereof. A conductor 40 of that winding is connected to the end portion 12 of the electric fuse 26 of FIGS. I-6; and the end portion 20 of that electric fuse is connected to a conductor 42 which will extend to the exterior of the winding 38 for connection to an electric circuit. Although the end portions 12 and 20 of the electric'fuse-26 could be connected to the conductors 40 and 42 of FIG. 8 in various ways, those end portions will preferably be connected to those conductors by welding.

The function and operation of the electric fuse 26 in FIG. 8 will be essentially identical to the function and operation of the identically-numbered electric fuse in FIG. 7. If the average temperature within the winding 38 in FIG. 8 is less than the average temperature within the frying pan 28 in FIG. 7, the expansion and contraction of the fusible element 11 in the electric fuse 26 of FIG. 8 will be less than the expansion and contraction of the fusible element of the identically-numbered electric fuse of FIG. 7; but if the average temperature within the winding 38 in FIG. 8 is greater than the average temperature within the frying pan 28 in FIG. 7, the expansion and contraction of the fusible element 11 in the electric fuse 26 of FIG. 8 will be greater than the expansion and contraction of the fusible element of the identically-numbered electric fuse of FIG. 7. However in either event, the electric fuse 26 of FIG. 8 will continuously carry its rated current, and yet be able to respond to a predetermined overload or to a short circuit to open the circuit. Also, because the fusible element 11 of that electric fuse is a metal stamping of rectangular cross section, the elongated portion 16 of that fusible element will deflect in a plane which is perpendicular to the wide surfaces of that portion. Further, because both ends of the tubular casing 24 of FIG. 8 are open, the fusible element 11 can freely expand and contract relative to that tubular casing. Additionally, because the end portions 12 and 20 of that fusible element are wider than the inner diameter of the tubular casing 24, those end portions limit movement of that fusible element axially of that tubular casing. Furthermore, because the widths of the intermediate portions 14 and 18 are close to the inner diameter of the tubular casing 24, those intermediate portions will coact with the inner surfaces of the ends of that tubular casing to define small semicylindrical spaces through which gases and metal vapors would have to flow as they escaped from that tubular casing. Moreover, the desired radius of the inner surface of the tubular casing 24 is equal to or greater than the square root of the sum of (-w/2 +[(D/2) -l-T/2)] where T is the thickness of the fusible element 11, where W is the width of the intermediate portion 14, and where D is the maximum deflection which the longitudinal center of the portion 16 could experience if the edges of the uppermost surface of that portion were in engagement with one side of the inner surface of the tubular casing 24 prior to the start of the deflection and if the edges of the lowermost surface of that portion were in engagement with the opposite side of the inner surface of that tubular casing at the conclusion of that deflection. As a result, repeated elongations and contractions of the fusible element of the electric fuse 26 of FIG. 8 wil not impair or adversely affect that fusible element.

Referring to FIG. 9, the numeral 44 denotes a capacitor which has metal foils wound between thin layers of insulating material. The numeral 46 denotes an enclosure for the capacitor 44; and the numeral 48 denotes one of the'terminals of that capacitor. That terminal extends through, but is suitably insulated from, the top of the enclosure 46; and the numeral 50 denotes a conductor which extends to one of the metal foils of that capacitor. The end portion 12 of the electric fuse 26 of FIG. 9 is connected to the inner end of the terminal 48, and the end portion 20 of that electric fuse is connected to the conductor 50. Although the end portions 12 and 20 of the electric fuse 26 of FIG. 9 could be secured to the terminal 48 and to the conductor 50 in various ways, those end portions will preferably be secured to that terminal and to that conductor by weld- The function and operation of the electric fuse 26 in FIG. 9 will be essentially identical to the-function and operation of the identically-numbered electric fuse in FIG. 7. However, the average temperature within the enclosure 46 in FIG. 9 should be appreciably lower than the average temperature within the frying pan 28 in FIG. 7. Regardless of the average temperature within that enclosure, the electric fuse 26 in FIG. 9 will be able to continuously carry its rated current, and yet be able to respond to a short circuit or to a predetermined overload to open the circuit. Also, because the fusible element of that electric fuse is a metal stamping of rectangular cross section, the elongated portion of that fusible element will deflect in a plane which is perpendicular to the wide surfaces of that portion. Further, because both ends of the tubular casing of FIG. 9 are open, the fusible element of the electric fuse 26 can freely expand and contract relative to that tubular casing. Additionally, because the end portions of that fusible element are wider than the inner diameter of the tubular casing, those end portions limit movement of that fusible element axially of that tubular casing. Furthermore, because the widths of the intermediate portions of the fusible element of the electric fuse 26 are close to the inner diameter of the tubular casing, those intermediate portions will coact with the inner surfaces of the ends of that tubular casing to define small semicylindrical spaces through which gases and metal vapors would have to flow as they escaped from that tubular casing. Moreover, the desired radius of the inner surface of the tubular casing is equal to or greater than the square roof of (w/2) +[(D/2) +(T/2)]" where T is the thickness of the fusible element, where w is the width of one of the intermediate portions of the fusible element of the electric fuse 26, and where D is the maximum deflection which the longitudinal center of the reduced cross section portion of that fusible element could experience if the edges of the uppermost surface of that portion were in engagement with one side of the inner surface of the tubular casing prior to the start of the deflection and if the edges of the lowermost surface of that portion were in engagement with the opposite side of the inner surface of that tubular casing at the conclusion of that deflection. As a result, repeated elongations and contractions of the fusible element of the electric fuse 26 of FIG. 9 will not impair or adymeL tthat a me t.

Referring to FIG. 10, the numeral 51 denotes a stiff conductor which is disposed within the envelope of an electric lamp, and the numeral 53 denotes a similar conductor. The end portion 12 of the fusible element of an electric fuse 26 is welded to the conductor 51, while the end portion 20 of that fusible element is welded to the conductor 53. The weak spot, not shown,

and the major portions of the lengths of the intermediate portions 14 and 18 of that fusible element are encased by the tubular casing 24 of that electric fuse. The conductors 51 and 53 will connect that electric fuse in series relation with the light-generating component, not shown, of that electric lamp.

The function and operation of the electric fuse 26 in FIG. 10 will'be essentially identical to the function and operation of the identically-numbered electric fuse in FIG. 7. However, the average temperature within the envelope of the electric lamp may be appreciably higher than the average temperature within the frying pan 28 in FIG. 7. Regardless of the average temperature within that envelope, the electric fuse 26 in FIG. 10 will be able to continuously carry its rated current and yet be able to respond to a short circuit or to a predetermined overload to open the circuit. Also, because the fusible element of that electric fuse is a metal stamping of rectangular cross section, the reducedcross section portion of that fusible element will deflect in a plane which is perpendicular to the wide surfaces of that portion. Further, because both ends of the tubular casing 24 of FIG. 10 are open, the fusible element of the electric fuse 26 can fully expand and contract relative to that tubular casing. Additionally, because the end portions of that fusible element are wider than the inner diameter of the tubular casing 24, those end portions limit movement of that fusible element axially of that tubular casing. Furthermore, because the widths of the intermediate portions 14 and 18 are close to the inner diameter of the tubular casing 24, those intermediate portions will coact with the inner surfaces of the ends of that tubular casing to define small semicylindrical spaces through which gases and metal vapors would have to flow as they escaped from that tubular casing. Moreover, the desired radius of the inner surface of the tubular casing 24 is equal to or greater than the square root of the sum of (w/2) [D/2) +(T/2)] where T is the thickness of the fusible element of electric fuse 26, where W is the width of the intermediate portion 14, and where D is the maximum deflection which the longitudinal center of the reduced cross-section portion of that fusible element could experience if the edges of the uppermost surface of that portion were in engagement with one side of the inner surface of the tubular casing 24 prior to the start of the deflection and if the edges of the lowermost surface of that portion were in engagement with the opposite side of the inner surface of that tubular casing at the conclusion of that deflection. As a result, repeated elongations and contractions of the fusible element of the' electric fuse 26 of FIG. will not impair or adversely affect that fusible element.

Referring to FIG. 11, the numeral 52 generally denotes a fusible element which has a terminal-like end portion 54, a terminal-like end portion 56, intervening intermediate portions 55 and 57, and a portion of reduced cross section. Those intermediate portions and that portion of reduced cross section preferably are identical tothe intermediate portions 14 and 18 and the portion 16, respectively, of the fusible element 11 of FIGS. 1-6. Further, the terminal-like end portion 54 can be identical to the terminal-like end portion 12 of the fusible element 11. However, the terminal-like end portion 56 differs from the terminal-like end portion 20 of the fusible element 11, in that it has a width which is no greater than that of the contiguous intermediate portion. The terminal-like end portion 56 will initially lie in' the plane which is defined by the terminal-like end portion 54, the intermediate portions 55 and 57, and the portion of reduced cross section. However, after the terminal-like end portion 56 has been telescoped through a tubular casing 58 of insulating material, that terminal-like end portion will be bent at an appreciable angle to the-axis of that tubular casing; and, thereafter, that bent terminal-like end portion will limit shifting of the fusible element 52 to the left, and the wide terminal-like end portion 54 will limit shifting of that fusible element to the right. In this way, the fusible element 52 will prevent accidental separation thereof from the tubular casing 58 of the insulating material even though the terminal-like end portion 56 has a width less than the inner diameter of that tubular cas- Referring to FIG. 12, the numeral 60 generally denotes a fusible element which has terminal-like end portions 62 and 64 which can be essentially identical to the terminal-like end portion 56 of the fusible element 52 in FIG. Ill. The fusible element 60 has intervening intermediate portions and a portion of reduced cross section which can be identical to the intermediate portions 14 and 18 and to the portion of reduced cross sec-' tion 116 of the fusible element 11 of FIGS. 1-6. Initially, the terminal-like end portions 62 and 64 will lie in the plane which is defined by the intermediate portions and by the portion of reduced cross section of the fusible element 60. However, after that fusible element has been telescoped through a tubular casing 66 of insulating material, the terminal-like end portions 62 and 64 will be bent away from the axis of that tubular casing at appreciable angles. Thereafter, those terminal-like end portions will prevent accidental separation of that tubular casing material from that fusible element. In FIG. 12, the terminal-like end portions 62 and 64 are shown as being bent so they extend in the same direction from the plane which is defined by the intermediate portions and the portion of reduced cross section of the fusible element but those terminal-like end portions could be bent in opposite directions relative to that plane.

The function and operation of each of the electric fuses of FIGS. 11 and 12 will be essentially identical to the function and operation of the electric fuse in FIG. 7. However, the average temperature within the installation where either of the electric fuses of FIGS. 11 and 12 is operated may be higher or lower than the average temperature within the frying pan 28 in FIG. 7. Regardless of the average temperature within that installation, each of the electric fuses of FIGS. 11 and 12 will be able to continuously carry its rated current, and yet be able to respond to a short circuit or to a predetermined overload to open the circuit. Also, because the fusible element of each of those electric fuses is a metal stamping of rectangular cross section, the portion of reduced cross section of that fusible element will deflect in a plane which is perpendicular to the wide surfaces of that portion. Further, because both ends of the tubular casings 58 and 66, respectively, in FIGS. 11 and 12 are. open, the fusible element in each of those tubular casing can freely expand and contract relative to that tubular casing. Additionally, because the end portion 54 is wider than the inner diameter of the tubular casing 58 and because the end portion 56 is bent at an appreciable angle to the axis of that tubular casing, those end portions limit movement of the fusible element 52 of FIG. 11 axially of that tubular casing. Similarly, because the end portions 62 and' 64 of the fusible element 60 of FIG. 12 are bent at appreciable angles to the axis of the tubular casing 66, those end portions limit movement of that fusible element axially of that tubular casing. Furthermore, because the widths of the intermediate portions of each of the fusible elements 52 and 60 are close to the inner diameters of the tubular casings for those fusible elements, those intermediate portions will coact with the inner surfaces of the ends of those tubular casings to define small semi-cylindrical spaces through which gases and metal vapors would have to flow as they escaped from those tubular casings. Moreover, the desired radius of the inner surfaces of each of the tubular casings 58 and 66 is equal to or greater than the square root of the sum of (w/2 +[(D/2) +(T/2)] where T is the thickness of the fusible element in that tubular casing, where W. is the width of the intermediate portion of that fusible element which is closest to the inner surface of that tubular casing, and where D is the maximum deflection which the longitudinal center of the reduced cross section portion of that fusible element could experience if the edges of the uppermost surface of that portion were in engagement with one side of the inner surface of the tubular casing prior to the start of the deflection and if the edges of the lowermost surface of that portion were in engagement with the opposite side of the inner surface of that tubular casing at the conclusion of that deflection. As a result,

repeated elongations and contractions of the fusible element 52 of the electric fuse of FIG. 1 1 or of the fusible element 60 of FIG. 12 will not impair or adversely affect either of those fusible elements.

Referring to FIGS. 13-16, the numeral 68 generally denotes a fusible element which has terminal-like end portions 70 and 72 and an elongated portion of constant width; and that elongated portion serves as the weak spot for that fusible element. The terminal-like end portions 76 and 72 can be identical to the terminallike end portions 12 and 20 of the fusible element 11 of FIGS. 1-6; and, prior to the time the fusible element 68 is assembled with a tubular casing 74 of insulating material; the terminal-like end portion 72 of that fusible element can be given a U-shaped cross section which is similar to the U-shaped cross section given the terminal-like end portion 20 in FIGS. 1 and 2. That U- shaped cross section will enable the terminal-like end portion '72 to be telescoped through the tubular casing 74 of insulating material; and, after that terminal-like end portion has been telescoped through that tubular casing, that terminal-like end portion can be planished to flatten it and'to give it the flat configuration shown in FIGS. 13-16. The terminal-like end portions 70 and 72 are suitably secured, as by spot welds, to stiff conductors 76 and 78; and those conductors are parts of an electric circuit to be protected by the electric fuse of which the fusible element 68 is a part.

The function and operationof the electric fuse in FIGS. 13-16 will be essentially identical to the function and operation of the electric fuse 26 in FIG. 7. However, because the fusible element 68 does not have intermediate portions, the elongated portion of that fusible element will be the portion, if any, of that fusible element which will deflect into engagement with the inner surface of the tubular casing 74, as indicated by FIGS. and 16. The average temperature within the space where the electric fuse of FIGS. 13-16 is operated may be higher or lower than the average temperature within the frying pan 28 in FIG. 7. Regardless of the average temperature within that space, that electric fuse will be able to continuously carry its rated current, and yet be able to respond to a short circuit or to a predetermined overload to open the circuit. Also, because the fusible element of that electric fuse is a metal stamping of rectangular cross section, the elongated portion of that fusible element will deflect in a plane which is perpendicular to the wide surfaces of that portion. Further, because both ends of the tubular casing 74 are open, the fusible element 68 can freely expand and contract relative to that tubular casing. Additionally, because the end portions 70 and 72 of that fusible element are wider than the inner diameter of the tubular casing 74, those end portions limit movement of that fusible element axially of that tubular casing. Furthermore, because the width of the elongated portion of the fusible element 68 is close to the inner diameter of the tubular casing 74, that elongated portion will coact with the inner surfaces of the ends of that tubular casing to define small semi-cylindrical spaces through which gases and metal vapors would have to flow as they escaped from that tubular casing. Moreover, the desired radius of the inner surface of the tubular casing 74 is equal to or greater than the square root of the sum of (w/2) +[(D/2) +(T/2) where T is the thickness of the fusible element 68, where D is the maximum deflection which the longitudinal center of the elongated portion could experience if the edges of the uppermost surface of that portion were in engagement with one side of the inner surface of the tubular casing 74 prior to the start of the deflection and if the edges of the lowermost surface of that portion were in engagement with the opposite side of the inner surface of that tubular casing at the conclusion of that deflection. As a result, repeated elongations and contractions of the fusible element of the electric fuse of FIGS. 13-16 will not impair or adversely affect that fusible element.

Because the terminal-like end portions of the various electric fuses of the present invention must be permanently connected to the conductors of the circuits to be protected by those electric fuses, any replacing of any of those electric fuses must be done by a skilled person. Such a skilled person would know that before he replaced any of the electric fuses hereof which had opened the circuit, he would have to service the frying pan, coil, capacitor or other electrical device in which that electric fuse had been incorporated. In some instances, the nature and the price of the electric device may be such that the said electrical device will be discarded when the electric fuse therein responds to a short circuit to open.

The shoulders between the intermediate portions 14 and 18 and the reduced cross section portion 16 of the fusible element 11 of FIGS. 1-6 are shown as being normal to the axis of that fusible element. Similarly, the shoulders between the intermediate portions and the reduced cross section portions of the fusible elements 52 and 68 of FIGS. 11 and 12 are shown as being normal to the axis of that fusible element. Moreover, the shoulders between the end portions 70 and 72 and the reduced cross section portion of the fusible element 68 of FIGS. 13-16 are shown as being normal to the axis of that fusible element. However, if desired, those shoulders can be disposed at any desired angles relative to the axes of those fusible elements. The inner surfaces of the various tubular casings 24, 58, 66 and 74 have been considered to be circular in cross section; but those inner surfaces could, if desired, be acircular in cross section. In the latter event, the D'in the formula which has been recited hereinbefore would be the diameter of a circle that was constructed so it would, prior to any deflection of any portion of the fusible element, pass through the upper edges of the uppermost surface of that portion of the fusible element which experienced the greatest deflection and would, at the conclusion of such deflection, pass through the lower edges of the lowermost surface of that portion.

Whereas the drawing and accompanying description have shown and described several preferred embodiments of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

What I claim is:

1. A small, inexpensive electric fuse which comprises an elongated fusible element in the form of a metal stamping of unitary form and of rectangular crosssection and an enclosure for said fusible element in the fon'n of an elongated but shorter, open-ended, tubular casing of insulating material, said fusible element having end portions that, at least in part, extend from and project outwardly beyond the ends of said tubular casing of insulating material to serve as terminals, said fus ible element having a portion of reduced cross section intermediate said end portions that serves as a weak spot, said end portions of said fusible element extending from and projecting outwardly beyond said ends of said tubular casing of insulating material as terminals that are securable to conductors of an electric circuit, said tubular casing of insulating material being telescoped over said portion of reduced cross section of said fusible element, said tubular casing of insulating material having an inner diameter which is sufficiently larger than the width of said portion of reduced cross section of said fusible element to permit free relative movement of said portion of reduced cross section of said fusible element axially of said tubular casing of insulating material as that length of said fusible element which is intermediate said conductors of said electric circuit elongates and contracts relative to said tubular casing of insulating material in proportion to the relative thermal coefficients of expansion of the materials of said fusible element and of said tubular casing of insulating material in response to increases and decreases in the temperatures of said fusible element and of said tubular casing of insulating material, said fusible element being bendable adjacent said ends of said tubular casing of insulating material to accommodate, at least in part, elongation of said length of said fusible element which is intermediate said conductors of said electric circuit and which occurs in proportion to said thermal coefficient of expansion of said material of said fusible element in response to increases in the temperature of said fusible element, said inner radius of said tubular casing of insulating material being at least as as?! 2 sq rsr of E Sum of (Wlfian (D/2) (T12) where T is the thickness of said fusible element, where W is the width of that part .of said fusible element which is disposed within said tubular casing of insulating material and which would be the first part of said fusible element that could respond to de flection of said fusible element, toward the inner surface of said tubular casing of insulating material, to engage said inner surface of said tubular casing of insulating material, and where D is the maximum deflection which said part of said fusible element could experience if the edges of the uppermost surface of said part of said fusible element were in engagement with one side of said inner surface of said tubular casing of insulating material prior tothe start of said deflection and if the edges of the lowermost surface of said part of said fusible element were in engagement with the opposite side of said inner surface of said tubular casing of insulating material at the conclusion of said deflection.

2. A small, inexpensive electric fuse as claimed in claim 1 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein said intermediate portions are wider than'said portion of reduced cross section, and wherein each of said intermediate portions coacts with the adjacent open end of said tubular casing of insulating material to define narrow cross-section passages at the opposite faces of said intermediate portion which can cool any gases and metal vapors that pass outwardly through said adjacent open end of said tubular casing of insulating material as said portion of reduced cross section blows. I

3. A small, inexpensive electric fuse as claimed in claim 1 wherein each of said end portions has a configuration which enables said end portion to coact with the adjacent end of said tubular casing of insulating material to limit axial movement of the contiguous portion of said fusible element inwardly of said end of said tubular casing of insulating material, whereby said end portions coact with said ends of said tubular casing of insulating material to limit axial shifting of said tubular casing of insulating material relative to said portion of reduced cross section.

4. A small, inexpensive electric fuse as claimed in claim 1 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein said intermediate portions are wider than said portion of reduced cross section, and wherein said first part of said fusible element that could respond to deflection of said fusible element, toward the inner surface of said tubular casing of insulating material, to engage said inner surface of said tubular casing of insulating material is on one of said intermediate portions.

5. A small, inexpensive electric fuse as claimed in claim 1 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, and wherein said bending which occurs adjacent said ends of said tubular casing of insulating material occurs in said intermediate portions.

6. A small, inexpensive electric fuse which comprises an elongated fusible element in the form of a metal stamping of unitary form and an enclosure for said fusible element in the form of an elongated but shorter, open-ended, tubular casing of insulating material, said fusible element having end portions that, at least in part, extend from and project outwardly beyond the ends of said tubular casing'of insulating material to serve as terminals, said fusible element having a portion of reduced cross section intermediate said end portions that serves as a weak spot, said end portions of said fusible element extending from and projecting outwardly beyond said ends of said tubular casing of insulating material as terminals that are securable to conductors of an electric circuit, said tubular casing of insulating material being telescoped over said portion of reduced cross section of said fusible element, said tubular casing of insulating material having an inner diameter which is sufficiently larger than the width of said portionof reduced cross section of said fusible element to permit free relative movement of said portion of reduced cross section of said fusible element axially of said tubular casing of insulating material as that length of said fusible element which is intermediate said conductors of said electric circuit elongates and contracts relative to said tubular casing of insulating material in proportion to the relative thermal coefficients of expansion of the materials of said fusible element and of said tubular casing of insulating material in response to increases and decreases in the temperatures of said fusible element and of said tubular casing of insulating material, said fusible element being bendable to accommodate, at least in part, elongation of that length of said fusible element which is intermediate said conductors of said electric circuit and which occurs in accordance with said thermal coefi'icient of expansion of said material of said fusible element in response to increases in the temperature of said fusible element, each of said end portions having a configuration which enables said end portion to coact with the adjacent end of said tubular casing of insulating material to limit axial movement of the contiguous portion of said fusible element inwardly of said end of said tubular casing of insulating material,

whereby said end portions coact with said ends of said tubular casing of insulating material to limit axial shifting of said tubular casing of insulating material relative to said portion of reduced cross section.

7. A small, inexpensive electric fuse as claimed in claim 6 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein said intermediate portions are wider than said portion of reduced cross section and wherein each of said intermediate portions coacts with the adjacent define narrow end of said tubular casing of insulating material to efmenarrow crosssection passages at the opposite faces of said intermediate portion which can cool any gases and metal vapors that pass outwardly through said adjacent open end of said tubular casing of insulating material as said portion of reduced cross section blows.

8. A small, inexpensive electric fuse as claimed in claim 6 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein said intermediate portions are wider than said portion of reduced cross section, and wherein the first part of said fusible element that could respond to deflection of said fusible element, toward the inner surface of said tubular casing of insulating material, to engage said inner surface of said tubular casing of insulating material is on one of said intermediate portions.

9. A small, inexpensive electric fuse as claimed in claim 6 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, and wherein at least part of said bending which occurs in said fusible element occurs in said intermediate portion.

MD. A small inexpensive, electric fuse as claimed in claim 6 wherein each of said end portions of said fusible element has a width greater than the inner diameter of said tubular casing of insulating material and wherein one of said end portions is temporarily formed to enable it to telescope through said tubular casing of insulating material and is thereafter re-formed so it can not be telescoped through said tubular casing of insulating material.

11.. A small inexpensive, electric fuse as claimed in claim 6 wherein one of said end portions of said fusible element has a width greater than the inner diameter of said tubular casing of insulating material, herein the other of said end portions is initially given a configuration enabling it to be telescoped through said tubular casing of insulating material, and wherein said other of said end portions is subsequently given a configuration enabling it to prevent the telescoping thereof back through said other of said end portions.

12. A small inexpensive, electric fuse as claimed in claim 6 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein at least one of said end portions is initially generally aligned with said intermediate portions so said one end portion can be telescoped through said tubular casing of insulating material, and wherein said one end portion is subsequently bent so it extends transversely of said tubular casing of insulating material to prevent the telescoping thereof back through the other end of said tubular casing of insulating material. i

13. A small inexpensive, electric fuse as claimed in claim 6 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein at least one of said end portions is initially generally aligned with said intermediate portions so said one end portion can be telescoped through said tubular casing of insulating material, wherein a part of said one end portion is subsequently bent outwardly beyond the periphery of said tubular casing of insulating material, wherein a part of the other of said end portions is bent ouwardly beyond the periphery of said tubular casing of insulating material, and wherein said outwardly-bent parts of said end portions limit axial telescoping of said fusible element relative to said tubular casing of insulating material.

14. A small, inexpensive electric fuse which comprises an elongated fusible element in the form of a metal stamping of unitary form and of rectangular cross-section and an enclosure for said fusible element in the form of an elongated but shorter, open-ended, tubular casing of insulating material, said fusible element having end portions that, at least in part, extend from and project outwardly beyond the ends of said tubular casing of insulating material to serve as terminals, having a portion of reduced cross section spaced inwardly from said end portions that serves as a weak spot, and having intermediate portions that are contiguous with and that extend axially outwardly from said portion of reduced cross section to merge into said end portions, each of said intermediate portions having a cross section larger than the cross section of said portion of reduced cross section, said end portions extending axially outwardly from said intermediate portions to be securable to conductors of an electric circuit, said tubular casing of insulating material being telescoped over and completely enclosing said portion of reduced cross section and also being telescoped over and completely enclosing a substantial portion of the length of each of said intermediate portions but leaving both of said end portions exposed, said tubular casing of insulating material having an inner diameter which is sufficiently larger than the width of either of said intermediate portions to permit free relative movement of said portion of reduced cross section and of said intermediate portions axially of said tubular casing of insulating material as that length of said fusible element which is intermediate said conductors of said electric circuit elongates and contracts relative to said tubular casing of insulating material in proportion to the relative thermal coefficients of expansion of the materials of said fusible element and of said tubular casing of insulating material in response to increases and decreases in the temperatures of said fusible element and of said tubular casing of insulating material, said tubular casing of insulating material having an inner diameter which is just slightly larger than the width of either of said intermediate portions so each of said intermediate portions coacts with the adjacent open end of said tubular casing of insulating material to define narrow cross-section passages at the opposite faces of said intermediate portion which can cool any gases and metal vapors that pass outwardly through said adjacent open end of said tubular casing of insulating material as said portion of reduced cross section blows, each of said end portions having a configuration which enables said end portion to coact with the adjacent end of said tubular casing of insulating material to limit axial movement of the contiguous intermediate portion inwardly of said end of said tubular casing of insulating material,

occurs in proportion to the thermal coefficient of expansion of said material of said fusible element in response to increases in the temperature of said fusible element, and wherein one of said intermediate portions will keep said portion of reduced cross section from engaging the inner surface of said tubular casing of insulating material. 

1. A small, inexpensive electric fuse which comprises an elongated fusible element in the form of a metal stamping of unitary form and of rectangular cross-section and an enclosure for said fusible element in the form of an elongated but shorter, open-ended, tubular casing of insulating material, said fusible element having end portions that, at least in part, extend from and project outwardly beyond the ends of said tubular casing of insulating material to serve as terminals, said fusible element having a portion of reduced cross section intermediate said end portions thAt serves as a weak spot, said end portions of said fusible element extending from and projecting outwardly beyond said ends of said tubular casing of insulating material as terminals that are securable to conductors of an electric circuit, said tubular casing of insulating material being telescoped over said portion of reduced cross section of said fusible element, said tubular casing of insulating material having an inner diameter which is sufficiently larger than the width of said portion of reduced cross section of said fusible element to permit free relative movement of said portion of reduced cross section of said fusible element axially of said tubular casing of insulating material as that length of said fusible element which is intermediate said conductors of said electric circuit elongates and contracts relative to said tubular casing of insulating material in proportion to the relative thermal coefficients of expansion of the materials of said fusible element and of said tubular casing of insulating material in response to increases and decreases in the temperatures of said fusible element and of said tubular casing of insulating material, said fusible element being bendable adjacent said ends of said tubular casing of insulating material to accommodate, at least in part, elongation of said length of said fusible element which is intermediate said conductors of said electric circuit and which occurs in proportion to said thermal coefficient of expansion of said material of said fusible element in response to increases in the temperature of said fusible element, said inner radius of said tubular casing of insulating material being at least as great as the square root of the sum of (W/2)2 and ((D/2) +(T/2))2 where T is the thickness of said fusible element, where W is the width of that part of said fusible element which is disposed within said tubular casing of insulating material and which would be the first part of said fusible element that could respond to deflection of said fusible element, toward the inner surface of said tubular casing of insulating material, to engage said inner surface of said tubular casing of insulating material, and where D is the maximum deflection which said part of said fusible element could experience if the edges of the uppermost surface of said part of said fusible element were in engagement with one side of said inner surface of said tubular casing of insulating material prior to the start of said deflection and if the edges of the lowermost surface of said part of said fusible element were in engagement with the opposite side of said inner surface of said tubular casing of insulating material at the conclusion of said deflection.
 2. A small, inexpensive electric fuse as claimed in claim 1 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein said intermediate portions are wider than said portion of reduced cross section, and wherein each of said intermediate portions coacts with the adjacent open end of said tubular casing of insulating material to define narrow cross-section passages at the opposite faces of said intermediate portion which can cool any gases and metal vapors that pass outwardly through said adjacent open end of said tubular casing of insulating material as said portion of reduced cross section ''''blows.''''
 3. A small, inexpensive electric fuse as claimed in claim 1 wherein each of said end portions has a configuration which enables said end portion to coact with the adjacent end of said tubular casing of insulating material to limit axial movement of the contiguous portion of said fusible element inwardly of said end of said tubular casing of insulating material, whereby said end portions coact with said ends of said tubular casing of insulating material to limit axial shifting of said tubular casing of insulating material relative to said portion of reduced cross section.
 4. A small, iNexpensive electric fuse as claimed in claim 1 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein said intermediate portions are wider than said portion of reduced cross section, and wherein said first part of said fusible element that could respond to deflection of said fusible element, toward the inner surface of said tubular casing of insulating material, to engage said inner surface of said tubular casing of insulating material is on one of said intermediate portions.
 5. A small, inexpensive electric fuse as claimed in claim 1 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, and wherein said bending which occurs adjacent said ends of said tubular casing of insulating material occurs in said intermediate portions.
 6. A small, inexpensive electric fuse which comprises an elongated fusible element in the form of a metal stamping of unitary form and an enclosure for said fusible element in the form of an elongated but shorter, open-ended, tubular casing of insulating material, said fusible element having end portions that, at least in part, extend from and project outwardly beyond the ends of said tubular casing of insulating material to serve as terminals, said fusible element having a portion of reduced cross section intermediate said end portions that serves as a weak spot, said end portions of said fusible element extending from and projecting outwardly beyond said ends of said tubular casing of insulating material as terminals that are securable to conductors of an electric circuit, said tubular casing of insulating material being telescoped over said portion of reduced cross section of said fusible element, said tubular casing of insulating material having an inner diameter which is sufficiently larger than the width of said portion of reduced cross section of said fusible element to permit free relative movement of said portion of reduced cross section of said fusible element axially of said tubular casing of insulating material as that length of said fusible element which is intermediate said conductors of said electric circuit elongates and contracts relative to said tubular casing of insulating material in proportion to the relative thermal coefficients of expansion of the materials of said fusible element and of said tubular casing of insulating material in response to increases and decreases in the temperatures of said fusible element and of said tubular casing of insulating material, said fusible element being bendable to accommodate, at least in part, elongation of that length of said fusible element which is intermediate said conductors of said electric circuit and which occurs in accordance with said thermal coefficient of expansion of said material of said fusible element in response to increases in the temperature of said fusible element, each of said end portions having a configuration which enables said end portion to coact with the adjacent end of said tubular casing of insulating material to limit axial movement of the contiguous portion of said fusible element inwardly of said end of said tubular casing of insulating material, whereby said end portions coact with said ends of said tubular casing of insulating material to limit axial shifting of said tubular casing of insulating material relative to said portion of reduced cross section.
 7. A small, inexpensive electric fuse as claimed in claim 6 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein said intermediate portions are wider than said portion of reduced cross section and wherein each of said intermediate portions coacts with the adjacent define narrow end of said tubular casing of insulating material to efinenarrow cross-section passages at the opposite faces of said intermediate portion which can cool any gases and metal vapors that pass outwardly through sAid adjacent open end of said tubular casing of insulating material as said portion of reduced cross section ''''blows.''''
 8. A small, inexpensive electric fuse as claimed in claim 6 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein said intermediate portions are wider than said portion of reduced cross section, and wherein the first part of said fusible element that could respond to deflection of said fusible element, toward the inner surface of said tubular casing of insulating material, to engage said inner surface of said tubular casing of insulating material is on one of said intermediate portions.
 9. A small, inexpensive electric fuse as claimed in claim 6 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, and wherein at least part of said bending which occurs in said fusible element occurs in said intermediate portion.
 10. A small inexpensive, electric fuse as claimed in claim 6 wherein each of said end portions of said fusible element has a width greater than the inner diameter of said tubular casing of insulating material and wherein one of said end portions is temporarily formed to enable it to telescope through said tubular casing of insulating material and is thereafter re-formed so it can not be telescoped through said tubular casing of insulating material.
 11. A small inexpensive, electric fuse as claimed in claim 6 wherein one of said end portions of said fusible element has a width greater than the inner diameter of said tubular casing of insulating material, herein the other of said end portions is initially given a configuration enabling it to be telescoped through said tubular casing of insulating material, and wherein said other of said end portions is subsequently given a configuration enabling it to prevent the telescoping thereof back through said other of said end portions.
 12. A small inexpensive, electric fuse as claimed in claim 6 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein at least one of said end portions is initially generally aligned with said intermediate portions so said one end portion can be telescoped through said tubular casing of insulating material, and wherein said one end portion is subsequently bent so it extends transversely of said tubular casing of insulating material to prevent the telescoping thereof back through the other end of said tubular casing of insulating material.
 13. A small inexpensive, electric fuse as claimed in claim 6 wherein said fusible element has portions that are intermediate said portion of reduced cross section and said end portions, wherein at least one of said end portions is initially generally aligned with said intermediate portions so said one end portion can be telescoped through said tubular casing of insulating material, wherein a part of said one end portion is subsequently bent outwardly beyond the periphery of said tubular casing of insulating material, wherein a part of the other of said end portions is bent ouwardly beyond the periphery of said tubular casing of insulating material, and wherein said outwardly-bent parts of said end portions limit axial telescoping of said fusible element relative to said tubular casing of insulating material.
 14. A small, inexpensive electric fuse which comprises an elongated fusible element in the form of a metal stamping of unitary form and of rectangular cross-section and an enclosure for said fusible element in the form of an elongated but shorter, open-ended, tubular casing of insulating material, said fusible element having end portions that, at least in part, extend from and project outwardly beyond the ends of said tubular casing of insulating material to serve as terminals, having a portion of reduced cross section spaced inwardly from said end portions that serves as a weak spot, and haviNg intermediate portions that are contiguous with and that extend axially outwardly from said portion of reduced cross section to merge into said end portions, each of said intermediate portions having a cross section larger than the cross section of said portion of reduced cross section, said end portions extending axially outwardly from said intermediate portions to be securable to conductors of an electric circuit, said tubular casing of insulating material being telescoped over and completely enclosing said portion of reduced cross section and also being telescoped over and completely enclosing a substantial portion of the length of each of said intermediate portions but leaving both of said end portions exposed, said tubular casing of insulating material having an inner diameter which is sufficiently larger than the width of either of said intermediate portions to permit free relative movement of said portion of reduced cross section and of said intermediate portions axially of said tubular casing of insulating material as that length of said fusible element which is intermediate said conductors of said electric circuit elongates and contracts relative to said tubular casing of insulating material in proportion to the relative thermal coefficients of expansion of the materials of said fusible element and of said tubular casing of insulating material in response to increases and decreases in the temperatures of said fusible element and of said tubular casing of insulating material, said tubular casing of insulating material having an inner diameter which is just slightly larger than the width of either of said intermediate portions so each of said intermediate portions coacts with the adjacent open end of said tubular casing of insulating material to define narrow cross-section passages at the opposite faces of said intermediate portion which can cool any gases and metal vapors that pass outwardly through said adjacent open end of said tubular casing of insulating material as said portion of reduced cross section ''''blows,'''' each of said end portions having a configuration which enables said end portion to coact with the adjacent end of said tubular casing of insulating material to limit axial movement of the contiguous intermediate portion inwardly of said end of said tubular casing of insulating material, whereby said end portions coact with said ends of said tubular casing of insulating material to limit axial shifting of said tubular casing of insulating material relative to said portion of reduced cross section.
 15. A small, inexpensive electric fuse as claimed in claim 14 wherein said intermediate portions are bendable to accommodate, at least in part, elongation of that length of said fusible element which is intermediate said conductors of said electric circuit and which occurs in proportion to the thermal coefficient of expansion of said material of said fusible element in response to increases in the temperature of said fusible element, and wherein one of said intermediate portions will keep said portion of reduced cross section from engaging the inner surface of said tubular casing of insulating material. 